I saw where someone had posted a link to a chart that showed the optimum
CO2 (I think). I've just started adding CO2 to my 155g tank the other day
and I've got the PH stable at 7.0 with 2dKH and 5dGH . Odd thing is, at
night, the CO2 turns off w/ the lights, but my PH stays the same.... I'm
running at about 2 bubbles per second on the CO2. OK, so on to the
question(s):

1) Is the PH supposed to change??

2) Are the KH and GH ok at this level?

3) How long should it take before I notice a difference in the plants?